Oxygen plays a vital role in the breathing processes and in the metabolism of the living organisms. Probably, the only living cells that do not need oxygen are some anaerobic bacteria that obtain energy from other metabolic processes.

In the human body, the oxygen is absorbed by the blood stream in the lungs, being then transported to the cells where an elaborated change process takes place. The nutrient compounds, inside of the cell, are oxidized through complex enzymatic processes. This oxidation is the source of energy of most of the animals, mainly of mammals. The products are carbon dioxide and water, which are eliminated by the body through the lungs.

The oxygen is useful in the treatment of pneumonia, emphysema, some heart disturbances, and another diseases. Sometimes hyperbaric oxygen chambers are used to treat poisoning victims by carbon monoxide or by anaerobic bacteria in the breathing system. The oxygen can increase the effects of the radiation in the cancerous cells, so that this treatment should be made in hyperbaric oxygen chambers. The use of atmospheres extremely rich in oxygen increases the fire risk, so rigorous precautions should be taken in these conditions.